Accurate navigation is thought to depend on neural representations of location and directional heading, which are carried by head direction cells, place cells, and grid cells. Head direction cells depend more heavily [than place cells] on signals from the otolith organs, but no studies have investigated the otolithic contribution to grid cell activity. Spatial deficits associated with otolith dysfunction may therefore result from disrupted head direction and/or grid cell activity. The proposed studies will test the otolithic contributionto entorhinal cortical grid cell activity during visual and non-visual navigation tasks. Results will provide important insight into the roles of vestibular information in neural representations of space, and the roles of these representations in navigation. A thorough understanding of the vestibular contribution to neural representations of space may enable new treatment approaches for cognitive deficits resulting from vestibular pathology.